Not Applicable.
Not Applicable.
1. Field of the Invention
The present invention generally relates to systems and methods for the economical management of hydrocarbon reserves located beneath the ocean floor. More particularly, the present invention relates to a general service vessel adapted to perform all well servicing operations and a floating buoy connected to a composite riser extending to one or more subsea well heads. In a different aspect, the present invention relates to methods for servicing deepwater hydrocarbon fields.
2. Description of the Related Art
Programs for recovering hydrocarbon reserves from beneath the ocean floor are now commonplace. Like their land-based counterparts, an offshore oilfield may have one or more wells extending into a subterranean formation. Additional equipment and facilities, however, are required to conduct offshore well operations because these wells are beneath hundreds or perhaps thousand of feet of water. A typical prior art offshore drilling and production system suitable for recovering subsea hydrocarbon reservoirs in an ocean environment is illustrated in FIG. 1.
Generally, a conventional offshore drilling and production system includes an operations facility 10 at the ocean""s surface 12 and production equipment 14 located at the mudline 16 on the ocean floor. In a deepwater field, i.e., where the water is too deep to establish a foundation on the ocean floor for a platform, a floating facility 10, such as a floating rig or semi-submersible vessel, is used to conduct drilling and intervention operations. Equipment at the mudline 16 can include a subsea wellhead system 18 for supporting concentric tubular pipe strings, such as casing and tubing 22, within a subsea wellhead 24 with the casing 20 and tubing extending into the well bore 26. A steel marine riser 28 extends from to the subsea wellhead 24 to the floating platform 10.
In prior art systems, the floating platform 10 is towed to a location generally above a subsea field. Thereafter, the floating platform is used as a base to drill, complete, produce and possibly workover one or more wells. Typically, the floating platform remains at this location for the duration of the productive life of the subsea field. This floating platform continues to be used for later well servicing operations, such as well stimulation, intervention, workover and drilling of lateral bores. Floating platforms are generally massive structures that are designed to withstand decades of service in a harsh ocean environment. Often, these floating platforms must meet rigid safety codes imposed by the controlling governmental authority. Thus, as is well known, it is not uncommon for floating platforms to cost upwards of one billion dollars to construct and bring into service.
Because of the enormous capital cost associated with a floating platform, well owners must be selective in planning and developing deepwater fields. Often, only those fields that have the potential to produce hydrocarbons in sufficient quantity to offset this capital outlay can be targeted for exploitation. This substantial capital outlay not only reduces the number of eligible fields, but also reduces the profitability of each field ultimately selected.
As is also well known, well operators typically optimize the floating platform to perform particular well operations such as drilling and logging efforts associated with the early phases of well construction and completion. After one or more well bores are drilled and completed, the general configuration of the floating platform remains largely unchanged even though later completion, intervention, and workover operations for the wells may be more easily performed by a different configuration.
These prior art well construction and management systems have several drawbacks. For example, because each deepwater field must be individually capable of hydrocarbon production rates sufficient to support at least one dedicated floating platform, many fields, incapable of meeting this threshold profitability requirement, are left undeveloped. Additionally, platforms are usually designed for well construction, a phase taking up only a handful of years in the production life of the well that may last for decades. Thus, for much of the service life of a well, these expensive platforms are less than optimal for well production, workover, intervention and other servicing operations. For example, the lifting and handling equipment and layout of a floating platform may be well suited to drill, case and cement a well bore, but ill suited to carry out frac or stimulation operations or specialized drilling operations.
Another drawback is that well intervention and servicing operations can be performed only after personnel, equipment, and material have been transported to the floating platform. The preparations for initiating these operations often includes contacting a land-based supply center, ordering the needed equipment and materials, having these items packed and shipped to the well site, unpacking these items at the offshore well site, and stowing these items until they are needed. Thus, the logistics for well servicing operations on a distant offshore floating platform are complex and require an additional expense.
The present invention overcomes the deficiencies of the prior art.
The present invention optimizes the configuration of the support structures used in each phase of the hydrocarbon recovery process, including well construction, production, intervention and work over. A exemplary deepwater field may include one or more wells having a wellhead and a well telemetry system that receives electrical signals from sensors and equipment in the well. A preferred embodiment of the present invention features a riser, a floating buoy and a service vessel.
The riser is formed of fatigue-resistant composite material and preferably includes embedded wiring that connects with the well telemetry system. The riser has a first end connected to a wellhead and a second end connected to the buoy. The buoy has a floating or semi-submersible hull that includes a hatch covering a moonpool. The riser passes through the moonpool and connects to the hull generally below the buoy hatch. In the preferred embodiment, the buoy includes telecommunication hardware and computer systems in communication with the well telemetry system via the riser embedded wiring. The service vessel has a bay in which the buoy docks during servicing operations. The service vessel is preferably a self-contained facility having all the personnel, equipment and materials necessary to carry out any number of well servicing operations. Service vessel personnel deploy the equipment and material into the riser via the buoy hatch.
A preferred method of the present invention includes towing a floating drilling rig buoy into a deepwater field to support initial well construction activity. After a well has been drilled and mudline equipment, such as a wellhead and the like, has been installed, the floating drilling rig platform is towed away to support well operations elsewhere. In its place, the floating buoy is stationed at the water""s surface generally above the wellhead. The well environment can be remotely monitored using the buoy communication system. When desired, the service vessel is dispatched to the deepwater field to perform one or more servicing operations. The service vessel docks with the buoy and draws the buoy into the bay of the vessel. Thereafter, service personnel deploy the necessary equipment and material into the riser via the buoy hatch. Once servicing operations are complete, the service vessel casts off the buoy and sails to the next buoy or field.
Thus, the present invention presents a number of advantages over the prior art. For example, a deepwater field no longer requires a dedicated floating rig; thus, the floating drilling rig can be utilized for a number of offshore oilfields saving cost. Moreover, because the buoy is mechanically and structurally less complex than the floating rig, expenditures on upkeep and maintenance are minimized. Furthermore, because the buoy is much less expensive than a floating rig, the financial loss of a buoy due to weather or accident is not as severe. Even further, the self-contained service vessel eliminates the need to pack, unpack, ship, and stow equipment and material.
Other objects and advantages will be apparent from the following description and claims.